This project was initiated to develop micromethods for the measurement of normally occurring biogenic amines, receptors and enzymes; to localize these amines and receptors and enzymes in peripheral tissues and specific brain nuclei and determine the effect of hypertension, endocrine manipulation and psychotropic drugs. Phenylethanolamine was found to be present in the nervous system of Aplysia. Selective increases in GAD (glutamic acid decarboxylase) occurred in the ipsilateral caudate and substantia nigra after chemical lesion of A9 and A10, indicating a relationship between the GABAergic and dopaminergic pathways. The dopamine-sensitive adenylate cyclase in the substantia nigra is localized outside the dopaminergic cells. Inhibition of catecholamine synthesis results in changes of serotonin metabolism in selective raphe nuclei. The activity of the adrenaline-forming enzyme, PNMT, is relatively high in the septal area. BIBLIOGRAPHIC REFERENCES: Saavedra, J.M., Grobecker, H., and Axelrod, J.: Biochemical and morphologic study of catecholamine metabolism in spontaneously hypersensitive rats. Mayo Clinic Proc. 52:391-394, 1977. Saavedra, J.M., Ribas, J., Swann, J., and Carpenter, D.O.: Phenylethanolamine: A New Putative Neurotransmitter in Aplysia. Science 195: 1004-1006, 1977.